The present invention relates to a reciprocating electromagnetic pump of the kind comprising a trunk piston of magnetic material so that the liquid to be delivered flows through it, said piston being reciprocable in a cylinder connected at its ends with the suction and delivery ducts and being enclosed in a coil energized during the piston suction stroke, during which a return spring is compressed, said spring driving back the piston during the delivery stroke when the energizing current is cut off, said energizing coil being AC fed, for instance through a diode so as to cause the current to flow only the direction in which the electromagnetic force generated between coil and piston, moves the latter in the suction direction.
The pumps of this kind generally have two valves at the delivery side, the one on the delivery duct and the other arranged on the piston head so as to close, in the positive pumping stage, its cavity and to cause it to pump the liquid which in the piston descent stage passed from the bottom part of the cylinder (suction side) to its top part (delivery side), as well as a suction valve which is closed in the piston descent stage and opens in the ascent stage, so as to fill with liquid the part of the cylinder emptied by the piston during its ascent stage.
In the known pumps of this kind, the cylinder in which the piston is reciprocated generally consists of several elements, that is a suction portion, a central portion in which the piston of magnetic material is being moved and a delivery portion into which goes the front part of the piston so as to cause compression and delivery of the liquid.
However this kind of pumps is very noisy, particularly when they are fixed to the structure of the machine on which they are operating, making an annoying hum together with likewise troublesome vibrations which one believes are caused by forces acting transversally to the direction of movement of said piston.
Moreover, because of the generation of the well known eddy currents, the pump has the tendency to get very warm so as to absorb an amount of electric power which is considerably higher than that required for the pump operation and is irreversibly transformed into heat.
Some manufacturer tried to find a remedy for the vibrations with particularly sophisticated and precise structures, which however solved only partially this problem, but left totally unsolved the hum and heating problem, so that the manufacturer are compelled to recommend not to use these pumps in a continuous way.